Geometrically, the pivot point of an occupant's hip rotation and the pivot point of reclining back are misaligned. As the occupant is positioned in the upright position and then reclined to a horizontal position (or alternatively referred to as a supine position), the distance from the occupant's back and hamstrings contract or decrease. When starting from the horizontal position and moved to the upright position the distance from the occupant's back and hamstrings expands or increases.
Prior patents have addressed only half the problem by developing various systems that allow for a sliding type movement of the back rest. Some of those prior patents include and are not limited to U.S. Pat. Nos. 6,296,265 to Lovins—Oct. 2, 2001; 5,634,688 to Ellis—Jun. 3, 1997; 5,549,357 to Counts et al.—Aug. 27, 1996; 5,261,725 to Rudolph—Nov. 16, 1993; 5,823,621 to Broadhead—Oct. 20, 1998; 5,297,021 to Koerlin et al.—Mar. 22, 1994; and 6,409,265 to Koerlin et al.—Jun. 25, 2002.
Currently manufactured devices that recline tend to force the occupant forward when positioned from the recline to the upright position due to the friction against the occupant's back which in turn pushes the occupant's buttocks forward thereby creating a sliding effect. Those currently produced chairs address only some of the desired positioning needs of users and clinicians without regard to shear forces. The current method of dealing with shear has been the use of different support surfaces that merely mask or at best buffer some of the shear.
The aim of the invention is to mitigate these issues with a device that responds to the various forces applied to the occupant's skin.